Method and apparatus for making tubes



H. B. ANDREWS Er AL 08 METHOD AND APPARATUS FOR MAKING TUBES Filed Dec. 1936 s 4 I 1W0 m m 2 1.1 zwllfim .01 5 a! wfi IIJW March 14, 1939,

March 14, 1939. H. B. ANDREWS ET AL PPARATUS FOR MAKING TUBES Filed Dec. 23, 1936 4 v d c& 65

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Patented Mar. 14, 1939 METHOD AND APPARATUS FOR MAKING UBES Herbert B. Andrews and James R. Haines, Battle Creek, Mich., assignors to American Stamping Company, Battle Creek, Mich., a corporation of Michigan Application December 23, 1936, Serial No. 117,401

11 Claims.

This invention is a novel method of and means for producing a drawn metal tube, for use as a piston pin or the like, by controlling the fiow of metal around punches during successive 5 drawing operations to thin the walls and to create an internal taper in each end of the tube.

One object is to produce such a tube out of drawn metal, and during the drawing operation to produce an internal taper in each end of such tube.

Another object is to provide novel means for cutting the blank from a strip of sheet metal, drawing such blank into a cup, and drawing such cup into a preliminary shell by one operation of triple die and coacting axially disposed plungers whereby we can accomplish the blanking and two drawing operations at one stroke of the plunger forcing the drawing punch through the die. 20 Another object is to insure the initial centering of the punch in the die in the first operation on the blank by making the die diameter equal to the punch diameter plus double thickness of metal.

Other objects of the invention will be hereinafter explained.

To impart a clear understanding of our invention We will explain the same with reference to the accompanying drawings which illustrate the several steps of our method and the dies and punches employed and also a novel product thereof.

In said drawings:-

Fig. 1 is a sectional view of a triple die and 0 cooperating punches, illustrating the operation of cutting a disk from a metal sheet.

Fig. 2 is a view of such die, illustrating the first drawing step of our method, in which the disk is formed into a cup-shaped blank.

Fig. 3 is a similar view of such die, illustrating the second drawing step of our method, in which the cup-shaped blank is converted into a tapered shell having a centering recess in its bottom.

Figs. 4, 5, 6 and 7 respectively show the several dies and cooperating punches employed in the successive third, fourth, fifth and sixth drawing operations on the shell.

Fig. 8 shows how the last drawn shell is cut to form the completed tubular pin.

Fig. 9 is a side view of the completed pin.

In carrying out our invention we first cut a disk from a sheet of metal of the desired thickness; and then in the first drawing operation convert such disk into a cup-shaped blank, without thinning the metal, and retaining uniform thickness of the metal in such blank. In the next drawing operation this cup-shaped blank is elongated and its side walls are tapered slightly from bottom upward.

Preferably we perform the aforesaid disk cutting operation and the first two drawing operations by means of a triple action die and double plunger as indicated in Figs. 1-3. The die block I has a bore whose upper end la corresponds in diameter and shape to the size and contour of the disk to be cut from the metal sheet. Cooperating with the upper portion la of the bore in die l is a tubular blanking punch 2 which will sever a disk m from a metal sheet M when the punch descends into the die. Below the portion la the bore of die I is reduced in diameter as at lb forming a die, and the disk m is forced through die lb by a punch 2a, which operates within the axial bore in punch 2. Punch 2a moves downward and after punch 2 stops, punch 2a continues its downward movement and draws the disk 121. into a cup-shaped blank S (as shown in Fig. 2). Below die lb the bore of die I is further reduced in diameter as at lo; and after punch 2a has formed the cup S, the punch 2a continues its downward movement and forces the cup S through the reduced portion lc of the bore and draws the cup into a shell S as shown in Fig. 3. The lower end of punch 2a is preferably tapered so that the shell S is slightly tapered internally from its lower end upward as shown in Fig. 3.

It will be seen that the triple die I and its 00- acting punches 2 and 20!. shown in Figs. 1 to 3 during the downward strokes of the punches cut a blank m (see Fig. 1), then draw the blank into a cup S (see Fig. 2), and then draw the cup into the shell S (see Fig. 3).

The blank m (Fig. 1) is cut the same thickness as the strip M and the part lb of the die and punch 2a are of such relative proportions that the annular space between their opposed walls is equal in width to the thickness of the blank m. In other words the diameter of the die is equal to the diameter of the punch plus a double thickness of the blank m. For instance, if the blank was cut out of a metal sheet or strip .140 gauge thick, and then drawn by a punch dropped onto the center of the blank through a die whose diameter is larger than the diameter of the punch, by an amount equal to two thicknessesof the metal disk, the resultant cup, created by drawing such disk through such die by such punch, is formed with walls .140 thick as the metal flows up around the punch into the annular space provided by the difference between 55 the diameters of the punch and die. While it is commonly assumed the punch will center in a die, we have found that unless the above diameters of the die and punch relative to the thickness of the metal blank are followed the metal will flow unequally around the punch due to soft or hard spots in the metal sheet as it comes from the rolling mill.

The metal of the cup S is of the original thickness of the metal sheet or strip M. In the first drawing operation the metal forms a bushing around the punch 2a of the same thickness as the original metal, and in such operation the metal is confined so accurately that in normal production the wall variation is only about .002 of an inch.

The punch 2a has a projection p on its lower end; and the diameter of such pojection is the same as the desired inside diameter of the finished tube. This projection p makes a central depression .9 in the inner surface of the bottom of the shell S; and every punch used in subsequent operations has a similar projection which engages such depression and thereby causes the punch in each subsequent operation to center itself exactly in the shell. This centering recess 8 in the closed end of the shell enables us to control the flow of metal evenly around the punches in subsequent steps.

In the second drawing operation the blank S is forced through die lc by being drawn through the reduced portion lc of the bore by a further downward movement of punch 20. as in Fig. 3. In this second drawing operation shell S is drawn into a hollow shell S closed at bottom and having its sides gradually lessened in thickness toward its upper end, as shown in Fig. 3. This manner of deep drawing and ironing or thinning of side walls of shell S enables us to produce the desired product.

The punches 2 and 2a. are operated in proper time and manner by any usual or suitable means; such means are well known in the art and will be readily understood by those familiar therewith and further illustration or description thereof is unnecessary.

The shell S retains the original thickness of metal at its bottom as it is drawn through the die lc. The more nearly this can be done, the less strain is set up on the metal as it forms upward and thins around punch.

The shell S produced by the second drawing operation (Fig. 3) has heavy metal on bottom and part way up side walls, but is thinner at top, and it also has the depression s in the center of its closed bottom for the purpose of centering the shell in subsequent operations as above stated.

The shell S produced by the second drawing operation (Fig. 3) is then re-drawn in a die 3, Fig. 4, by a punch 3b. The bore of die 3 is of less diameter than die [0, but its upper end So is enlarged to permit free fiow of metal in the upper end of the shell. The lower end 3d of punch 3b is slightly reduced in diameter and above this is a tapered portion 30. By means of die 3 and punch 3b the shell S (Fig. 3) is re-drawn into a' shell S2 (Fig. 4) which is left thick at the top forming a soft head portion s, which will prevent A fracture of the shell in subsequent draws. In this third drawing operation (Fig. 4) an internal taper s2 is produced below the top of shell, which begins the desired taper in the upper end of the final shell. The depression 8 created in shell S so that the resultant shell S2 is of even thickness around its periphery and of uniform diameter.

This third drawing operation (Fig. 4) produces a shell S2 longer but of smaller diameter than shell S. The thickness of metal below the taper s2 is retained same as in shell S.

The shell S2 produced by this third operation (Fig. 4) is then re-drawn in a die 4 (Fig. 5) by a punch 4b. The bore 411 of die 4 is slightly less in diameter than the bore of die 3, and it has a slight contracting taper 40 near its lower end, and its upper end is enlarged as at 4e to permit free fiow of metal at upper end of shell.

The shell S3 produced by this fourth drawing operation is longer than shell S2 but is reduced in diameter; its body and bottom are approximately of same thickness as the shell S2. The shell S3 retains the inside taper s2 and has a lower externally tapered portion 33 formed thereon by the tapered portion 40 of the die 4, preliminary to forming the outer taper on the lower end of the final shell and ultimate tube. Shell S3 also retains the depression 8.

The shell S3 produced by the fourthdrawing operation (Fig. 5) is then re-drawn, by means of a die 5 and punch 52) (Fig. 6), into a shell S4. The bore 5a of die 5 is less in diameter than the bore of die 4, and its lower portion is contractingly tapered as at 50 for a length equal to the desired final taper of the lower end of the final shell; and below this tapered portion the bore is reduced in diameter, for about an eighth of an inch, as at Sdto facilitate reversing of the taper on the lower end of the shell in the final drawing operation. The bore 5a is also enlarged at top, as at 5e to permit free fiow of metal at upper end of shell. The die 5 and punch 51) are so formed that during the fifth drawing operation the bottom of the shell remains of original thickness but its body is lengthened and further reduced in diameter, and its lower tapered portion is thinned and finished as at $4 to such dimension on outside of shell as will ensure proper taper on the inside of shell when such lower tapered portion is reversed during the next drawing operation. The shell S4 produced by this fifth drawing operation retains the inner taper $2 at its upper end. The interior taper s2 and exterior taper s4 are of the desired pitch, but one is inside and the other outside. The outside diameter of the extreme lower end' of' the shell S4 below tapered portion s4 is the same as the desired outside diameter of the final product.

The shell S4 produced by the fifth drawing operation (Fig. 6) is then subjected to the final drawing action of a die 6 and punch 6b (Fig. 7) The bore 6a of die 6 corresponds in diameter to the desired exterior diameter of the finished tubular pin and is less than the diameter of die 5, but its upper end is enlarged as at 66 to accommodate the head s on the upper end of the shell. The punch 6b is of a diameter corresponding to the desired internal diameter of the central portion of the finished pin. Punch 6b centers in depression 3 in bottom of shell S4 and the diameter of such shell is reduced by the action of the die 6; and during the last drawing opera tion the taper s4 on the outside of the bottom of shell S4 (Fig. 6) is transferred in the drawing of the shell through die 6 to the inside of the shell S5 (see Fig. '7). This transfer occurs because the bottom end of shell S4 (the diameter of which was established in the fifth drawing operation Fig. 6) is not touched and as the shell is lengthened, and its diameter reduced, its ex- 75 terior wall draws out straight or parallel and the metal in the lower tapered end of the shell shifts so that the taper s4 is transferred from the exterior to the interior of the resultant shell S5.

The recess s in the lower end of the successive shells is always the same diameter and is engaged by the small projection p on the lower end of the punches 2a, 3b, 4b! and 5b (Figs. 1 to 6) and by the end of the punch to (Fig. '7), which punch end is of the same diameter as the projections 19. In the last drawing operation the end of punch 6b fitting in recess s and the thickness of the closed end of the shell prevents collapse of the shell adjacent the lower end of the punch, and causes the lower end of the shell to expand to the diameter of the bore of die 6 in passing therethrough, thus transferring the taper $4 from outside to the inside of the shell.

The sixth and final drawing operation produces a shell S5 (Figs. 7 and 8) of uniform exterior diameter below the head s and having two internal tapers, one s! on inside near its bottom, and one 82 on inside near its top. The final shell S5 also has a flared head s6 at one end and its other end s5 is closed.

When intended for use as a piston pin, the head portion 88 and bottom end portion s5 of the shell S5 (see Fig. 8) are cut off on the lines c-c and dr--d, Fig. 8; and the remaining portion forms a tubular pin S6 (Fig. 9) having a straight outer wall and interior tapers s2, s! at opposite ends thereof as shown in Fig. 9.

The length of tube, thickness of walls, length of tapers, and all dimensions may be varied to suit specific requirements.

In the first and second drawing operations (Figs. 3 and 4) the shell passes through the die. In all subsequent drawing operations the shells do not pass through the dies and must be knocked out of the dies.

It will be seen that in the last four drawing steps we maintain a thick head or top portion 5' on the shell, which head prevents shell from cracking; and we also maintain the heavy wall thickness in the middle portions of the shells.

In our method we provide a depression in the bottom of the cup and each successive shell of a diameter corresponding to the desired internal diameter of the main body of the pin, and to ensure accurate centering of punches; also provide for free flow of surplus metal at the top of the successive shells to ensure workability of metal; and reverse the bottom taper from outside to inside of shell in the final drawing opera-' tion without the employment of a contracting or compressing die or an internalshaping punch.

We claim:-- 1

1. ,The method of drawing tubular pins from sheet metal, consisting in blanking a disk from sheet metal; drawing the disk into a cup; drawing the cup into a shell closed at one end; drawing the shell through a plurality of successive .dies, each oi,- less-diameter than the preceding such tapered portion during subsequent drawing operations.

3. In a method of drawing tubular pins as set forth in claim 1; forming an internal taper adjacent the upper portion of the shell during one 5 drawing operation and preserving and maintaining such tapered portion during subsequent drawing operations; and cutting off the ends of the shell at the outer extremities of the said tapers thereby providing a pin having an internal taper at each end thereof.

4. The method of drawing tubular pins from sheet metal, consisting in blanl ing a disk from sheet metal; drawing the disk into a cup; drawing the cup intd a shell closed at one end; drawing the shell through a plurality of successive dies, each of less diameter than the preceding die to reduce the shell in diameter and increase its Iengthpfand maintaining a head of metal on the open ends of the shells to permit free flow of metal and prevent cracking thereof during the drawing operation; 1 forming an external taper on the shell adjacent its closed end during one drawing operation, and transferring this taper from the exterior to the interior of the shell by drawing the shell through a straight die by a straight punch.-

5. The method of drawing tubular pins from sheet metal, consisting in blanking a disk from sheet metal; drawing the disk into a cup; drawing the cup'into' a shell closed at one end; drawing the shell through a plurality of successive dies, each of less diameter than the preceding die to reduce the shell in diameter and increase its lerigthfgjand maintaining a head of metal on the open ends of the shells to permit free flow of metal and prevent cracking thereof during the drawing 01981317109; forming an external taper on the upper portion of the shell during one drawing operation and preserving and maintaining such tapered portion during subsequent drawing operations.

6. In a method of drawing tubular pins as set forth in claim 2 forming an internal taper adjacent the'upper portion of the shell during one drawing operation and preserving and maintaining such tapered portion during subsequent drawing operations; and cutting ofiflthe ends of the shell at the outer extremities of the said tapers thereby providing a pin having an internal taper at each end thereof.

7. The method of drawing tubes from sheet metal; consisting in blankinga disk from a metal sheet, drawing the disk into a cup, drawing the cup into'a shell closed at one end and having a recess in the inside surface of its closed end corresponding in diameter to the desired final internal diameter of the body of the tube, reducing the shell in diameter and increasing its length by drawing the shell in successive dies, each of less diameter than the preceding die, by means of successive punches coacting respectively with the successive dies, each punch having its inner end formed to engage the recess in the shell and center the shell in the die during the drawing 65 operation,;and maintaining a head on the open end of the shell during the third and subsequent drawing operations to permit free flow of metal at the top of shell and prevent cracking thereof Z1 and forming an external taper on the shell ad- 70 jacent its closed end during one drawing operation, and transferring this taper from the exterior to the interior of the shell by drawing the shell through a straight die by a straight punch.

8. In the method of drawing metal tubes set 75 forth in claim 7; forming an external taper on the upper portion of the shell during one drawing operation and preserving and maintaining such tapered portion during subsequent drawing operations.

9. In a method of drawing tubular pins as set forth in claim 7; forming an internal taper adjacent'th'e upper portion of the shell during one drawing operation and preserving and maintaining such tapered portion during subsequent drawing operations; and gutting oiT the ends of the shell at the outer extremities of the said tapers thereby providing a pin having an internal taper at each end thereof.

10. In the method of drawing tubes from metal shells; forming an interior taper in the shell ad jacent the upper portion during one drawing operation and maintaining said taper during subsequent drawing operations; forming an exterior taper in the shell adjacent its closed end during one drawing operation and transferring this taper from the exterior to the interior of the shell during a subsequent drawing operation by drawing the shell through a straight die by means of a straight punch; and cutting off the ends of the shell at the outer extremities of said tapers thereby providing a tube having an internal taper at each end thereof.

11-. Means for drawing tubes from sheet metal, comprising a die having a bore formed with an upper portion corresponding to the shape of the blank to be cut from the sheet metal; and a contracted portion below its upper portion corresponding to the external diameter of the cup to be formed from said blank, and said bore also having a further contracted portion below the first contracted portion; a tubular punch cooperating with the upper portion of the die to sever a blank from a metal sheet; and a drawing punch axially disposed within the tubular punch and. adapted to successively force the blank through the first contracted portion to form a cup, and to then force the cupped blank through the lower further contracted portion to convert the cup into a shell, said drawing punch having a relatively long taper at its lower end whereby the walls of the shell will be thickest adjacent its closed end.

HERBERT B. ANDREWS. JAMES R. HAINES. 

